Summary Neuroscience has an essential requirement for large-scale neural recording and perturbation technologies for the understanding of brain function, as well as in the diagnosis and treatment of neurological disorders. At present, a large gap exists between the localized optical microscopy studies looking at fast neuronal activities at single cell resolution level and the whole-brain observations of slow hemodynamics and brain metabolism provided by the macroscopic imaging modalities. The proposed three- year project is aimed at developing a highly synergistic triple-modality platform combining acoustic stimulation with volumetric optoacoustic and planar fluorescence imaging to volumetrically monitor and perturb the activity of large, distributed neuronal populations with unprecedented spatiotemporal resolution. This goal will be accomplished by constructing a bi-directional interface based on a spherical matrix array transducer capable of both recording real-time three-dimensional optoacoustic tomographic data and acoustic phased array beam steering and holography for ultrasonic neural stimulation. The high temporal resolution in these volumetric recordings will make it possible to directly and indirectly track neural activity, with novel near- infrared calcium (Ca2+) sensors and intrinsic hemodynamic contrast, respectively. The resulting scanner will simultaneously record activity from large fields of view in scattering brains, including deep subcortical structures inaccessible by any light microscope. The plan of action includes screening of several potential candidates for Ca2+ imaging, including genetic and chemigenetic sensors. System validation will be performed in vivo in mice, aiming at establishing sensitivity and spatiotemporal resolution metrics in detecting Ca2+ relevant for sensory-based decision making. Finally, the complete system will be used to probe the link between neural activity and behavior by systematically characterizing the effects of image-targeted US perturbation in mice performing olfactory-guided tasks. In contrast to purely optical techniques, the proposed method is tailored for non-invasive deep brain observations and manipulations and is ideal for large fields of view and columnar-scale mesoscopic resolutions. !